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                <ol class="chapter"><li class="expanded "><a href="about.html"><strong aria-hidden="true">1.</strong> About</a></li><li class="expanded "><a href="howitworks.html"><strong aria-hidden="true">2.</strong> How it works</a></li><li class="expanded "><a href="quickstart.html"><strong aria-hidden="true">3.</strong> Quick start</a></li><li class="expanded "><a href="usage.html"><strong aria-hidden="true">4.</strong> Usage</a></li><li class="expanded "><a href="api.html" class="active"><strong aria-hidden="true">5.</strong> Contract API</a></li><li class="expanded "><a href="libsemaphore.html"><strong aria-hidden="true">6.</strong> libsemaphore</a></li><li class="expanded "><a href="trustedsetup.html"><strong aria-hidden="true">7.</strong> Trusted setup</a></li><li class="expanded "><a href="audit.html"><strong aria-hidden="true">8.</strong> Security audit</a></li><li class="expanded "><a href="creditsandresources.html"><strong aria-hidden="true">9.</strong> Credits and resources</a></li></ol>
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                        <h1><a class="header" href="#contract-api" id="contract-api">Contract API</a></h1>
<h2><a class="header" href="#constructor" id="constructor">Constructor</a></h2>
<p><strong>Contract ABI</strong>:</p>
<p><code>constructor(uint8 _treeLevels, uint232 _firstExternalNullifier)</code></p>
<ul>
<li><code>_treeLevels</code>: The depth of the identity tree.</li>
<li><code>_firstExternalNullifier</code>: The first identity nullifier to add.</li>
</ul>
<p>The depth of the identity tree determines how many identity commitments may be
added to this contract: <code>2 ^ _treeLevels</code>. Once the tree is full, further
insertions will fail with the revert reason <code>IncrementalMerkleTree: tree is full</code>.</p>
<p>The first external nullifier will be added as an external nullifier to the
contract, and this external nullifier will be active once the deployment
completes.</p>
<h2><a class="header" href="#add-deactivate-or-reactivate-external-nullifiiers" id="add-deactivate-or-reactivate-external-nullifiiers">Add, deactivate, or reactivate external nullifiiers</a></h2>
<p><strong>Contract ABI</strong>:</p>
<p><code>addExternalNullifier(uint232 _externalNullifier)</code></p>
<p>Adds an external nullifier to the contract. Only the owner can do this.
This external nullifier is active once it is added.</p>
<ul>
<li><code>_externalNullifier</code>: The new external nullifier to set.</li>
</ul>
<p><code>deactivateExternalNullifier(uint232 _externalNullifier)</code></p>
<ul>
<li><code>_externalNullifier</code>: The existing external nullifier to deactivate.</li>
</ul>
<p>Deactivate an external nullifier. The external nullifier must already be active
for this function to work. Only the owner can do this.</p>
<p><code>reactivateExternalNullifier(uint232 _externalNullifier)</code></p>
<p>Reactivate an external nullifier. The external nullifier must already be
inactive for this function to work. Only the owner can do this.</p>
<ul>
<li><code>_externalNullifier</code>: The deactivated external nullifier to reactivate.</li>
</ul>
<h2><a class="header" href="#insert-identities" id="insert-identities">Insert identities</a></h2>
<p><strong>Contract ABI</strong>:</p>
<p><code>function insertIdentity(uint256 _identityCommitment)</code></p>
<ul>
<li><code>_identity_commitment</code>: The user's identity commitment, which is the hash of
their public key and their identity nullifier (a random 31-byte value). It
should be the output of a Pedersen hash. It is the responsibility of the
caller to verify this.</li>
</ul>
<p><strong>Off-chain <code>libsemaphore</code> helper functions</strong>:</p>
<p>Use <code>genIdentity()</code> to generate an <code>Identity</code> object, and
<code>genIdentityCommitment(identity: Identity)</code> to generate the
<code>_identityCommitment</code> value to pass to the contract.</p>
<p>To convert <code>identity</code> to a string and back, so that you can store it in a
database or somewhere safe, use <code>serialiseIdentity()</code> and
<code>unSerialiseIdentity()</code>.</p>
<p>See the <a href="./usage.html#insert-identities">Usage section on inserting
identities</a> for more information.</p>
<h2><a class="header" href="#broadcast-signals" id="broadcast-signals">Broadcast signals</a></h2>
<p><strong>Contract ABI</strong>:</p>
<pre><code>broadcastSignal(
    bytes memory _signal,
    uint256[8] memory _proof,
    uint256 _root,
    uint256 _nullifiersHash,
    uint232 _externalNullifier
)
</code></pre>
<ul>
<li><code>_signal</code>: the signal to broadcast.</li>
<li><code>_proof</code>: a zk-SNARK proof (see below).</li>
<li><code>_root</code>: The root of the identity tree, where the user's identity commitment
is the last-inserted leaf.</li>
<li><code>_nullifiersHash</code>: A uniquely derived hash of the external nullifier, user's
identity nullifier, and the Merkle path index to their identity commitment.
It ensures that a user cannot broadcast a signal with the same external
nullifier more than once.</li>
<li><code>_externalNullifier</code>: The external nullifier at which the signal is
broadcast.</li>
</ul>
<p><strong>Off-chain <code>libsemaphore</code> helper functions</strong>:</p>
<p>Use <code>libsemaphore</code>'s <code>genWitness()</code>, <code>genProof()</code>, <code>genPublicSignals()</code> and
finally <code>genBroadcastSignalParams()</code> to generate the parameters to the
contract's <code>broadcastSignal()</code> function.</p>
<p>See the <a href="./usage.html#broadcast-signals">Usage section on broadcasting
signals</a> for more information.</p>

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